Anisotropy-driven velocity log reconstruction in deviated wells: A case study from deepwater Sadewa Field

Abstract

Deviated drilling is a common cost-cutting strategy used in efforts to develop deepwater hydrocarbon fields. By utilizing the existing platform, new wells are drilled with a particular inclination to reach the intended depth level as a branch of the main vertical well. Drilling at inclination results in a change in the direction of observation from data collection. This change will affect the measured magnitude value when well logging is carried out, especially on physical parameters sensitive to the direction of the measurement such as velocity. Distortion of velocity values due to the orientation effect of data collection has been a limiting factor in seismic analysis because of phase changes during the well-to-seismic tie, inconsistent amplitude variation with offset responses, and ambiguity in the appearance of the hockey stick effect on long-offset seismic data. The oil and gas industry is starting to move toward developing concepts that link the presence of anisotropy recorded in field data with the possibility of hydrocarbon reservoirs. Velocity logging (sonic and shear sonic) should begin to get more attention to support this strategy of making data retrieval results more precise. The motivation of this study is to apply the method of calculating velocity compensation values to reconstruct sonic and shear sonic logs in deviated wells by utilizing anisotropy parameters. By reconstructing the velocity log, the authors attempt to verticalize the log to return the log function to represent subsurface conditions.